Method and associated apparatus for distributed dynamic paging area clustering under heterogeneous access networks

ABSTRACT

In a telecommunication system, paging areas may be automatically reconfigured as required. Paging areas can be adaptively reconfigured in accordance with changes in movement traffic of mobile hosts. The system and method work under a constraint that only a limited number of area IDs are permitted for each paging unit area. Also, the system and method work over heterogeneous access networks. Thus, according to the presently disclosed embodiments, paging areas reconfigure themselves according to changes in movement traffic of mobile hosts.

RELATED APPLICATIONS

This application claims priority of U.S. provisional patent applicationSer. No. 60/327,091, filed Oct. 3, 2001 in the name of Daichi Funato,which is incorporated herein by reference.

BACKGROUND

The present invention relates generally to radio communication systems.More particularly, the present invention relates to a method andassociated apparatus for distributed dynamic paging area clusteringunder heterogeneous access networks.

As wireless technology and the Internet are commercially developed,mobile Internet access becomes more and more popular globally. In thedeveloping third generation and fourth generation (3G and 4G,respectively) wireless system, wireless and Internet technology will becombined together. In such systems, a mobile host is free to move abouta region while remaining in radio contact with a base station or otherfixed infrastructure access point. Each base station of a network servesmobile hosts in a geographic area surrounding the base station. As themobile host moves, communication with the mobile host is handed off fromone base station to another. Research and standardization efforts arecurrently underway with a goal to integrate both cellular technologiesand Internet technologies. Paging technology is one such technology.

Paging technology partitions all cells in a cellular system into severaldifferent areas called paging areas. A mobile host travelling acrossthese paging areas is required to register a new location whenever itmoves from one paging area to a different one. When the mobile host iswithin a paging area, its exact location is unknown to the system. As aresult, when a call arrives, the exact location of the called MH isdetermined by sending paging message to all cells of the MH's pagingarea. Paging technology has proven to be very effective to reduce thepower consumption at the mobile host.

Paging technology is used to track a mobile host (MH) that is in adormant mode. The mobile host enters the dormant mode when not activelycommunicating in order to conserve battery power. While in the dormantmode, however, a MH is capable of receiving a signal from a nearbyaccess point, reporting to it an area identifier (ID) indicating thepaging area where the MH is traveling. The paging area is the portion ofa network or system to which a paging signal intended for a particularMH is broadcast. While traveling from one paging area to another, the MHcan recognize if and when it crosses the boundary between paging areasand enters another paging area because it begins receiving a differentarea ID signal upon crossing the boundary. The MH, upon reception of thedifferent area ID signal, wakes up from the dormant mode to an activemode and sends a signal to register itself with the new paging area.

In 3G and 4G wireless systems, the backbone is assumed to be an InternetProtocol (IP) network. IP is a standardized communication formatapplicable to both wireless and wireline communication systems, or acombination of the two. An IP based paging protocol is necessary for 3Gand 4G wireless systems.

A challenge in the development of IP paging technology is how to assignpaging areas. Two issues have been identified with defining andarranging or configuring paging areas. The first issue is on the size ofa paging area. If each paging area is sized to be relatively large,significant network resources must be diverted to paging operationsconducted in that area. A paging signal must be broadcast extensively tocover the large area to locate just one MH. If each paging area isdefined to be relatively small, a significant amount of energy will beused in the MH for responding to paging signals. If paging areas aredefined to be relatively small, the MH will frequently cross a boundarybetween two adjacent paging areas. Each time the MH crosses a boundary,it has to wake up and register with a new area, dissipating batterypower.

The other issue in sizing paging areas is overlapping of paging areas.In current communications systems, each paging area is allowed to have alimited number of area IDs (usually one area ID). Some arrangements areneeded to dynamically define and arrange paging areas under thisconstraint on the number of area IDs that each paging area is allowed tohave.

Much existing research has been done on how to construct an appropriatepaging area. In one reference, it is proposed to use an individuallocation area concept that treats mobile user with different mobilityand call characteristics differently to reduce the average signalingcost of mobility management. Based on this concept, several approachessuch as a time-based strategy and profile-based strategy have beenintroduced for the cellular paging systems. However, all this researchhas been directed to design a static paging area which means the pagingarea construction will be fixed all the time. However, simulationresults show that such fixed paging area design will lead to a highpaging cost under many circumstances. This is because the user trafficvaries from time to time; a static paging area may not be able to coverthe traffic pattern well so that the location update cost increasessignificantly.

Current paging technology uses fixed paging areas. Paging areas aremanually defined and arranged, and once defined and arranged, they areseldom changed. These manually defined paging areas are thus inflexibleand cannot adapt themselves to changes in communication traffic. Also,since paging areas are defined manually, human errors are unavoidable.Some proposals have been made on dynamic configuration of paging areas,but these proposals permit unlimited overlapping of area IDs. In theseproposals, each MH dynamically computes and shapes its optimal pagingarea size according to the traffic and movements. Naturally, each pagingarea overlaps in those individual paging schemes.

Much research has been done to optimize paging area configuration sothat the overall paging cost can be minimized. The total paging cost forthe system comes from two parts, location update cost and paging cost.The location update cost is the resource used to update the userlocation when the user moves into a new paging area. The paging cost isthe resource used to send messages to the user within each paging area.A properly designed paging area should be able to minimize the overallpaging cost.

A dynamic paging area construction algorithm has been proposed. Forexample, a dynamic method for configuring sizes and shapes of pagingareas, along with an individual location, has been proposed. However, itis difficult to control location area overlap in the proposed method.Paging area overlap has to be controlled in most cellular system such asthe Personal Digital Cellular (PDC) system in Japan, the Global Systemfor Mobile communication (GSM) and wideband code division multipleaccess (W-CDMA) systems. These wireless systems are designed tobroadcast a restricted number of paging area IDs per base station at atime. As a result, a base station can not belong to many location areassimultaneously.

Accordingly, there is a need for an improved paging area constructionmethod and apparatus.

BRIEF SUMMARY

By way of introduction only, in accordance with the presently disclosedembodiments, paging areas may be automatically reconfigured as required.Paging areas can be adaptively reconfigured in accordance with changesin movement traffic of mobile hosts. The system and method in accordancewith these embodiments work under a constraint that only a limitednumber of area IDs are permitted for each paging unit area. Also, thesystem and method work over heterogeneous access networks. Thus,according to the presently disclosed embodiments, paging areasreconfigure themselves according to changes in movement traffic of MHs.

The foregoing summary has been provided only by way of introduction.Nothing in this section should be taken as a limitation on the followingclaims, which define the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-6 are block diagrams of various embodiments of a radiocommunication network;

FIGS. 7 and 8 are block diagrams illustrating reconfiguration of pagingareas in a radio communication system;

FIG. 9 is a block diagram showing exemplary embodiments of a mobile hostand two last hop routers;

FIG. 10 is an operational block diagram of the paging clustering agentof FIG. 9;

FIGS. 11 and 12 illustrate organization of one embodiment of theprobability map of the paging area clustering agent of FIG. 9;

FIG. 13 shows an exemplary cluster map of the paging clustering agent ofFIG. 9;

FIG. 14 shows one embodiment of the format of default information in theexemplary cluster map of FIG. 13;

FIG. 15 shows one embodiment of the format of branch information in theexemplary cluster map of FIG. 13;

FIG. 16 shows one embodiment of the format of root information in theexemplary cluster map of FIG. 13;

FIG. 17 is an operational block diagram of the clustering process ofFIG. 10;

FIG. 18 is an operational block diagram of the paging forwardingfunction of FIG. 10;

FIG. 19 is an operational block diagram of the probability map updateprocess of FIG. 10;

FIG. 20 is an operational block diagram of the host reporter agent inthe mobile host of FIG. 9;

FIG. 21 illustrates clustering of paging areas represented by theirpaging area clustering agents;

FIGS. 22-26 illustrate clustering operations; and

FIGS. 27-35 illustrate communication during clustering operationprocedures.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

In systems that use paging, mobile hosts operate in one of two modes,active and dormant mode. When actively transmitting or receiving data,the mobile terminal is in an active state. In this state, the networkknows has location information for the mobile host and is ready todeliver data immediately. If the mobile host is inactive for a period oftime, it will change into a dormant mode. In dormant mode, the network'slocation information for the mobile host may be stale. If data arrivesin the network for the mobile host, the mobile host must first belocated before data can be delivered. This procedure of locating themobile host is broadly referred as paging.

Paging is beneficial for a mobile host because it reduces the amount oftime the mobile host is required to listen to the radio interface, whichdrains the mobile host's battery. Furthermore, paging reduces networksignaling costs by requiring the mobile host to signal only when itcrosses a paging area boundary rather than when it switches between basestations. The large amount of signaling for mobile terminal tracking isreduced when paging areas contain many base stations.

Referring now to the drawing, FIG. 1 is a block diagram of oneembodiment of a radio communication network 100. The network 100includes a first last hop router (LHR) 102, a second LHR 104, aplurality of access points (AP) 106, 108, 110 associated with the firstLHR 102 and a plurality of access points 112, 114, 116 associated withthe second LHR 104. A first mobile host (MH) 120 is in communicationwith the first plurality of access points 106, 108, 110 and a secondmobile host 122 is in communication with the second plurality of accesspoints 112, 114, 116. As used herein, communication may be wireline orwireless communication. One example of wireline communication is digitalcommunication according to TCP/IP. One example of wireless communicationis IP communication on a W-CDMA network.

The last hop routers 102, 104 are in communication with an internetprotocol (IP) network 118, which may be the Internet or a subnetwork.The last hop router is the edge router to which a mobile host may beconnected. A last hop router serves a last hop subnet (LHS). A last hopsubnet is the edge subnet to which a mobile host is directly connected.Thus, LHR 102 serves LHS 132 and LHR 104 serves LHS 134.

Access points 106, 108, 110, 112, 114, 116 are equipment that providespaging and access through a layer 2 connection to a mobile host within acell served by each respective access point. Examples of access pointsare base stations in a cellular or personal communication system (PCS)network. Thus, access point 106 serves a cell 136; access point 108serves a cell 138; access point 110 serves a cell 140; access point 112serves a cell 142; access point 114 serves a cell 144; and access point116 serves a cell 146.

A mobile host (MH) such as mobile hosts 120, 122 is a standard IP host,able to communicate with remote devices using internet protocol.Typically, a MH is battery powered so as to be mobile or portable. A MHfurther includes the ability to enter a dormant mode which is alow-power mode. The dormant mode is a state in which the MH restrictsits ability to receive normal IP traffic by reducing its monitoring ofradio channels. This allows the MH to save battery power and reducessignaling load on the network. Actual two way communication requiresexiting the dormant mode and return to an active mode.

The communication network 100 is configured to provide paging for mobilehosts in the network. Paging is signaling by the communication network100 through radio access points directed to locating a dormant mode MHand alerting it to establish a last hop connection. In a last hopconnection, the MH is in two-way communication with an AP. A paging areais a collection of radio access points that are actuated to locate adormant MH. A dormant mode MH may be required to signal to the networkwhen it crosses a paging area boundary so that the network can maintainan approximate location for the MH. A paging area cluster is acollection of paging areas which share a common paging area identifier.

A typical IP paging protocol operates as follows:

A. Registration

When a mobile host enters dormant mode or when it moves out of itscurrent paging area, it registers with a tracking agent (TA) of a basestation. A tracking agent is responsible for tracking a mobile host'slocation while it is in dormant mode or active mode, and for determiningwhen the mobile host enters active mode. Registration specifies themobile host's identity (home address for example) and the identifier ofits current paging area. Upon reception of a paging registration, the TAcreates an entry that binds the host's identity with the paging agent(PA) that is in charge of the paging area specified in the registration.A paging agent is responsible for alerting the mobile host when a packetarrives and the host is in dormant mode. It also sends a report to adormant monitoring agent (DMA) when the host has entered dormant mode.The dormant monitoring agent detects the delivery of packets to a hostthat is in dormant mode.

B. Packet Delivery

During the dormant period, if data arrives in the network for the mobilehost, the host must first be located before data can be delivered. Whenthe DMA receives packets for the host, it buffers them, since the hostis registered as dormant. The DMA then asks the TA for the host'scurrent PA. The TA in turn asks the PA to page the mobile host. The PAsends a paging request to all base stations in the network which belongto the PA. Finally, each base station broadcasts a radio transmissioncontaining the page on a downlink to the dormant mobile host. When themobile host wakes up from the dormant mode to the active mode, it sendsa response message in the on the uplink to the paging base station. Themobile host enters the active state and registers its current location.For example, the mobile host provides a care-of address to the DMA. TheDMA then forwards the packets to the registered mobile host.

C. Dynamic Paging Area Configuration

Proper design of paging areas is based on a tradeoff between pagingtraffic and location update traffic. As the size of the paging areaincreases, the paging cost increases and the location update costdecreases. On the other hand, as the size of the paging area decreases,the paging cost decreases and the location update cost increases. Ingeneral, paging traffic is proportional to the number of calls to basestations in the paging area, while location update traffic isproportional to the number of mobile hosts crossing paging area borders.

A dynamic paging area configuration algorithm must minimize the overallnetwork location updating and paging cost. Generally, paging traffic isless critical than location update traffic since a location updateaffects not only the radio resource, but the load of distributedlocation databases in TA as well.

In the description herein, it is assumed that beacon frames aretransmitted periodically or continuously from each base station or basestation router to allow mobile hosts to identify current locationinformation. The beacon frame must contain at least a Paging Area ID(PA-ID) and a Base Station ID (BS-ID).

A PA-ID indicates the current paging area. The PA-ID may change when thebase station changes its paging area. A BS-ID uniquely identifies a basestation. The BS-ID is fixed. It is assumed the PA-ID and BS-ID are thesame at the time of system initialization.

It is further assumed that a mobile host is able to listen to beaconsfrom base stations even if it is in its dormant mode. Furthermore, it isassumed that the mobile host is able to identify the BS-ID of the cellin which the mobile host currently located and save this information forthe later use.

It is further assumed that each base station router has capabilities ofa paging agent (PA) and a dormant monitoring agent (DMA). It is alsoassumed that the PA-ID and the BS-ID can be mapped to the layer-3address (IP address) of base station routers using layer-2 to layer-3mapping protocols such as Inter Access Point Protocol. That means an IPaddress of a BSR can be obtained from the beacon information.

The network communication protocol defines a message for movementtraffic sampling. A mobile host listens to beacons and can store thelatest beacon information. This stored data is used for pollination to anext base station. When a mobile host moves to another paging area, itwakes up from the dormant mode to the active mode and updates itslocation information to the TA and DMA through a transmission to a basestation. At that time, the mobile host contains the memory of theprevious beacons even if it was not registered to that base station. Amessage is defined to send the information to the new base station. Thenotification message contains the PA-ID and BS-ID of the previous basestation so that the new base station recognizes the origin of the mobilehost.

FIGS. 1, 2, 3, 4 and 5 show one example of a network with an exemplarypaging area. In FIG. 1, each LHR 102, 104, creates a last hop subnet inwhich three access points are deployed. Each respective AP defines arespective cell.

FIGS. 2-5 illustrate additional examples of networks with additionalexemplary paging areas. In FIG. 2, a network 200 includes a single LHR202 and one AP 204. A cell 206 is served by the AP 204. The LHR 202defines one LHS 208 and one paging area 210 coextensive with the LHS208. In FIG. 3, a network 300 includes one LHR 302 and two APs 304, 306.The AP 304 serves a cell 308 and the AP 306 serves a cell 310. The LHR302 and APs 304, 306 together define one LHS 312 and a coextensivepaging area 314.

In FIG. 4, a network 400 includes two LHRs 402, 404. The LHR 402 has twoassociated APs 406, 408. Each of the APs 406, 408 serves an associatedcell. Similarly, the LHR 404 has two associated APs 410, 412. Each ofthe APs 410, 412 serves an associated cell. The APs 406, 408 togethercreate an LHS 414. The APs 410,412 together create an LHS 416. All fourAPs 406,408, 410, 412 together create one paging area 418.

In the network 500 of FIG. 5, a LHR 502 has four associated APs 504,506, 508, 510. Each AP serves a respective cell. Each pair of APscreates a paging area. Thus, the pair of APs 504, 506 creates a pagingarea 512 and the pair of APS 508, 510 creates a paging area 514. Thepaging areas 512, 514 together form a LHS 516.

In the network 600 of FIG. 6, two LHRs 602, 604, in conjunction withthree access points 610, 612, 614, define a paging area 616. The AP 610is associated with a first access network 620. The AP 612 is associatedwith a second access network 622. The AP 614 is associated with a thirdaccess network 624. Each AP 610, 612, 614 services an associated cell,providing radio communication to mobile hosts within the associatedcell. The paging area 616 extends over portions of each of the accessnetworks 620, 622, 624.

Thus, paging areas may be arranged in any of a wide variety ofconfigurations. Paging areas may exist within and among last hopsubnetworks and within and among access networks. In accordance with theembodiments disclosed herein, paging areas may be dynamicallyreconfigured as required by system circumstances.

FIG. 7 is a block diagram illustrating reconfiguration of paging areasin a radio communication system. FIG. 7 shows a portion of a cellularradio communication network 700 positioned near a road 702. The network700 includes a plurality of access points serving cells such as cells704, 706, 708. Initially, each cell corresponds to a minimum pagingarea. Minimum paging areas are defined by circles with respect to theroad 702 as shown in the left drawing of FIG. 7. As radio traffic in thenetwork 700 increases along with vehicle traffic along the road 702,paging areas located along the road will be joined to define one largepaging area 710 as shown in the right drawing of FIG. 7. Subsequently,as traffic permits, paging areas may be ungrouped even to the point ofminimum paging areas such as in the left drawing of FIG. 7.

Preferably, paging areas are auto configured to minimize human effortand error. Paging areas are preferably well adapted to user movements toenhance paging efficiency in the network. Further, the method whichproduces this paging area clustering preferably provides a limitedoverlapping permission mechanism. Still further, the method of pagingarea clustering should be applicable across many heterogeneous accessnetworks.

FIG. 8 is a series of block diagrams illustrating another example ofpaging area clustering. FIG. 8 shows time variation in paging areas in aradio communication system 800. In the drawings of FIG. 8, each hexagonshows a minimum paging area. Combined or clustered paging areas havecommon fill patterns. Starting from the upper left drawing of FIG. 8,movement traffic of mobile hosts (MHs) from area c to area d increases.Movement of traffic of MHs is represented by the arrows within eachindividual drawings of FIG. 8. This depiction is a simplification oftraffic in an actual system. As a result of this traffic movement, aread adopts area c's area ID, and areas c and d become one paging area, asis shown by the changed fill of area d in the upper right drawing ofFIG. 8.

Subsequently, as shown in the upper right drawing, MH traffic increasesfrom area a to area b. As a result, area b adopts area a's area ID, andareas a and b become one paging area, as shown by the changed fill ofarea b. Subsequently, as shown in the lower right drawing of FIG. 8, MHtraffic increases from area b to area C. As a result, as shown in thelower left drawing, areas c and d adopt area b's area ID, and areas a,b, c and d become one large paging area. Thus, in this exemplaryembodiment, paging areas reconfigure themselves according to changes inmovement traffic of MHs.

FIG. 9 is a block diagram showing exemplary embodiments of a mobile host902 and two last hop routers 904, 906. Each of these devices and itscomponents will be describe below.

The mobile host (MH) 902 may be embodied, for example, as a cellular orPCS telephone, a personal digital assistant (PDA), a personal computer,or combinations of these or any other electronic devices. The mobilehost 902 includes a host reporter agent 908 and a layer 3 mobility agent910. In a typical embodiment, the mobile host 902 is embodied as amobile or portable electronic device including a battery, a processor,memory, a user interface and radio circuit. These components are notshown in FIG. 9 so as not to unduly complicate the drawing. The batteryprovides operating power for the MH 902. The processor may by amicroprocessor, microcontroller digital signal processor or other logicdevice or combination of devices which controls operation of the mobilehost 902. The processor operates in response to program instructionsstored in the memory, which may be semiconductor memory such as flash,EPROM or RAM. The user interface permits control of the mobile host 902by a user and may include a display, a keypad, a speaker and amicrophone or other components. The radio circuit permits radiocommunication with a remote device such as the last hop router 904. Theradio circuit in a typical embodiment includes a transmitter and areceiver which encodes and decodes, modulate and demodulate radiosignals, respectively. By means of the radio circuit, the mobile host902 communicates over a radio link 914 with the last hop router 904.

The host reporter agent 908 and the layer 3 mobility agent 910 areimplemented as software processes controlling operation andcommunication in the mobile host 902. The host reporter agent 908 isresponsible for reporting movement of the MH 902 to a paging areaclustering agent of a last hop router such as LHR 904, 906. The layer 3mobility agent 910 informs a dormant monitoring agent of a LHR of thearrival of an IP packet. The host reporter agent 908 and the layer 3mobility agent 910 will be described in greater detail below.

The last hop routers 904, 906 of the exemplary embodiment of FIG. 9include a paging area clustering agent 920, a dormant monitoring agent922, a local paging agent 924, a local tracking agent 926 and a layer 3mobility agent 928. In a typical embodiment, the last hop router 904,906 provides a radio or wireline link to mobile hosts such as MH 902.The link may include a wireline link to an access point such as acellular base station which is in radio communication with one or moreMHs. The last hop router 904, 906 further provides a wireline link toother network devices such as other routers. Communication with the lasthop router 904, 906 is preferably according to internet protocol (IP)but may be in accordance with any suitable data communication protocolor standard.

In an exemplary embodiment, the last hop router 904, 906 includes aprocessor, a memory and communication circuits. The processor may be amicroprocessor or other digital logic for controlling the operation ofthe last hop router 904, 906, but may be any suitable control circuit.The processor operates in conjunction with program instructions and datastored in the memory. Communication circuits provide communication ofdata and instructions between the last hop router 904, 906 and othernetwork devices. The processor, memory and the communication circuitsare not shown in FIG. 9 so as to not unduly complicate the drawingfigure.

In FIG. 9, the last hop router 904 and the last hop router 906 are shownas being substantially identical. However, it will be appreciated thatthese components may vary widely in their structure and operationdepending on their operational requirements.

The paging area clustering agent (PCA) 920 operates to receive movementreports from mobility reporter agents of mobile hosts in communicationwith last hop router 904, 906. A PCA is notified by a dormant monitoringagent (DMA) of a packet arrival to a mobile host and sends pagingclustering messages to the local paging agent (LPA) clusters. Once thePCA 920 receives positive or negative results from LPA clusters, the PCAnotifies the DMA. Structure and operation of the PCA 920 will bedescribed in greater detail below in conjunction with FIG. 10.

The dormant monitoring agent (DMA) 922 operates to detect the deliveryof packets to a MH such as the MH 902 that is in dormant mode and toinform the PCA 920 to page the MH. Dormant mode is a low power sleepmode which may be entered by the MH to conserve battery power in the MH.Once the PCA 920 has reported that a routable connection to a networksuch as the Internet exists to the MH, the DMA 922 arranges for deliveryof the packet to the MH. In addition, the MH may change a DMA as the MHchanges paging area.

The local paging agent 924 (LPA) is responsible for alerting a mobilehost such as the MH 902. Additionally, the LPA 924 maintains pagingareas by periodically wide casting information over the link to themobile host to identify the paging area. In this exemplary embodiment,each paging area can be served by multiple Laps.

The local tracking agent (LTA) 926 is responsible for tracking thelocation of a MH while it is in a same last hop subnet (LHS) when the MHis in either dormant mode or active mode. The layer 3 mobility agent 928can be a Mobile IP Home Agent or Foreign Agent as those terms areconventionally known. The layer 3 mobility agent 928 informs the DMA 922of the arrival of an IP packet.

The PCA 920, DMA 922, LPA 924, LTA 926 and layer 3 mobility agent 928are preferably software processes implemented on the last hop router904, 906. Suitable program code and data for performing these softwareprocesses may be stored in memory of the last hop router 904, 906 foroperation of a processor or other control circuit of the last hop router904, 906.

FIG. 10 is an operational block diagram of the paging area clusteringagent 920 of FIG. 9. The paging area clustering agent 920 in theexemplary embodiment includes a probability map (PMAP) 1002, a clustermap 1004, a probability map update process 1006, a clustering process1008 and a paging forwarding process. These components of the pagingarea clustering agent 920 are preferably embodied as software processesfor controlling a last hop router such as the LHR 904, 906 of FIG. 9.

The paging area clustering agent 920 maintains a probability map 1002 todecide which paging group the PCA 920 should join. The PCA 920 uses acluster map to maintain the relation to other paging area clusteringagents. The probability map update process (PUP) 1006 operates tomaintain the probability map 1002. The clustering process 1008 performsthe core functions of the paging area clustering agent 920. The pagingforwarding process (PFP) executes forward paging requests. Each of theseprocesses will be described in greater detail below.

FIGS. 11 and 12 illustrate organization of one embodiment of theprobability map 1002 of the paging area clustering agent 920 of FIG. 9.The PMAP 1002 includes a statistical record of past movement traffic ofMHs. In the PMAP 1002, each minimum paging area or paging unit area isdefined with two spatial variables (X, Y) as shown in FIG. 11.X={ξ₁, ξ₂, . . . ξ_(J)},where ξ₁ denotes the area ID of paging area i.Y={η₁, η₂, . . . ξ_(K)},where η₁ denotes the network address identifier (NAI) of paging area i.A NAI may be an IP address.

An example is illustrated in FIG. 12. Assume that in past operation ofthe network, the probability that MH traffic moved from (ξ₁, η₁) to (ξ₅,η₅) for a specific time period is 40%. The probability that MH trafficmoved from (ξ₂, η₂) to (ξ₅, η₅) is 30%. The probability that MH trafficmoved from (ξ₂, η₆) to (ξ₅, η₅) is 20%. The probability that MH trafficmoved from (ξ₈, η₈) to (ξ₅, η₅) is 10%. Accordingly, the PMAP 1002 has atable 1202 entitled “two dimensional map” on in FIG. 12. This twodimensional map table is converted into a table 1204 entitled “onedimensional map.” In conversion, probabilities of coming from the samepaging area IDs (ξ) are added. This one dimensional map indicates thatarea ID (ξ₅) should be changed to area ID (ξ₂) because, according thepast movement traffic statistics, MH traffic came most into that areafrom area (ξ₂). Thus, the PMAP 1002 tells which paging areas should bemerged together or which paging areas should be severed from each other.

FIG. 13 illustrates organization of the cluster map (CMAP) 1004 of thepaging area clustering agent 920 of FIG. 10. The CMAP 1004 maintainsinformation as to which paging area is currently joined to or belongs towhich area. As shown in FIG. 13, the cluster map 1004 stores three kindsof information: default information 1302; branch information 1304; androot information 1306. At the outset of operation, paging areas areindependent and not joined to any other areas.

FIG. 14 shows one embodiment of the format of the default information1302. The default information 1302 includes the paging area ID 1402 ofsuch an independent paging area. The default information 1302 furtherincludes the network address identifier (NAI) 1404 for the pagingclustering agent (PCA). The NAI is unique to the PCA and includes, forexample, its IP address.

FIG. 15 shows one embodiment of the format of the branch information1304. In this embodiment, the branch information 1304 includes the rootpaging identifier (PID) 1502 of the cluster group's paging clusteringagent, a network address identifier 1504 for a predecessor pagingclustering agent, and a list of network access identifiers 1506 forpaging cluster agents which may be successors to the current PCA.

FIG. 16 shows one embodiment of the format of the root information 1306.The root information 1306 includes a root paging identifier 1602, whichis preferably equal to the default PID for the paging clustering agent.The root information 1306 further includes a complete list 1604 ofnetwork address identifiers of possible successor paging area clusteringagents. In the list 1604, each nearest possible successor PCA hasassociated with it a list of adjacent PCA network address identifiers.Thus, the first entry 1606 in the list 1604 of FIG. 16 is a list 1608 ofpossible successor PCA NAIs. Similarly, the second entry 1610 in thelist 1604 includes a list 1612 of possible successor PCA NAIs. In thepreferred tree structure, entries of the list 1608 further includeassociated leaf PCA NAIs such as NAI 1614.

The branch information 1304 and root information 1306 may be explained,using the example of FIG. 8. Paging areas a, b, c and d all have thesame ID assigned to area a. Area a is called a root area and has theroot information. The root information indicates all of the paging areasthat belong to the root area, i.e., areas b, c and d, in a treestructure. Paging areas other than root areas have branch informationthat indicates an immediately preceding paging area and all of thesucceeding paging areas depending from it. Thus, for instance, area bhas branch information that indicates that the immediately precedingarea is a, and the succeeding areas are c and d.

FIG. 17 is an operational block diagram of the clustering process 1008of FIG. 10. The clustering process (CP) 1008 includes a candidate searchfunction (CSF) 1702, a clustering decision function (CDF) 1704, aclustering management function (CMF) 1706, paging monitoring function(PMF) 1708 and performance evaluation function (PEF) 1710. Based oninformation from the PMAP 1002, the CSF 1702 locates candidate pagingareas to be joined to or disjoined from other paging areas. The CDF 1704determines, among the located candidate paging areas, which paging areashould be really joined or disjoined. For example, a paging area that isallowed to have only one area ID and has already been joined to anotherarea cannot be joined to any other paging area unless it is disjoinedfrom the current area. The CDF 1704 may decide which area should bedisjoined from the current area and joined to another area. The CMF1706, based on the decisions made by the CDF 1704, updates the CMAP1004. The CMF 1706 also updates the CMAPs of other areas from which ithas just been disjoined and/or to which it has just been joined.

On the other hand, the PMF 1708 monitors information from the pagingforwarding process 1010 that indicates frequencies of paging, andinformation from the probability map update process 1006 that indicateschanges in MH traffic, i.e., how many MHs have moved from one area toanother. The PEF 1710 evaluates the size of the current paging areas. Ingeneral, if the number of paging operations has increased, the size ofthe paging areas should be decreased to reduce the total cost of pagingnetwork traffic. On the other hand, the size of the paging areas shouldbe increased if the movement traffic of MHs has increased.

FIG. 18 is an operational block diagram of the paging forwarding process1010 of FIG. 10. The paging forwarding process includes a CMAP discoveryfunction (CMDF) 1802, a paging forwarding function (PFF) 1804 and pagingnotification function (PNF) 1806. The CMDF 1802 receives a pagingtrigger packet from a dormant memory agent (DMA) operation 1808 andqueries the CMAP 1004 to determine to which area the packet should bedelivered. The determined area contains the MH to which the pagingtrigger packet was directed. The PFF 1804 forwards the paging triggerpacket to the area determined by the CMDF 1802. The PNF 1806 notifiesthe clustering process 1008 of frequencies of paging trigger packetsreceived from the DMA operation 1808.

FIG. 19 is an operational block diagram of the probability map updateprocess 1006 of FIG. 10. The probability map update process 1006includes a PMAP maintenance function (PMMF) 1902, a report acceptancefunction (PAF) 1904 and a movement notification function (MNF) 1406. ThePAF 1904 receives a registration signal from the host reporter agent(HRA) 908 in a MH 902 (FIG. 9). Notified by the PAF 1904, the PMMF 1902calculates statistics of MHs coming in and out and updates the PMAP1002. The MNF 1906 determines frequencies of MHs coming in and out andnotifies the clustering process 1008.

FIG. 20 is an operational block diagram of the host reporter agent (HRA)908 in a MH 902 (FIG. 9). The HRA includes a reporter process (REPF)2002, and a previous location table (PLT) 2004 and a current locationtable (CLT) 2006. As the MH travels, the REPF 2002 updates the both PLT2004 and CLT 2006 and registers the MH with a new area. The reporterprocess 2002 reports paging area movement to the current paging areaclustering agent. As is indicated in FIG. 20, the PLT 2004 stores thepaging identifier (PID) and the network access identifier (NAI) for theprevious paging area clustering agent. Similarly, the CLT 2006 storesthe paging identifier (PID) and the network access identifier (NAI) forthe current paging area clustering agent. When the MH moves to anotherpaging area, the reporter process 2002 moves the current location table2006 information to the previous location table 2004.

FIG. 21 illustrates clustering of paging areas represented by theirpaging area clustering agents (PCAs). A cluster 2102 has one PCA towhich all other PCAs in the cluster 2102 belong or are associated. Suchas PCA is called the root PCA 2104. The cluster 2102 also has PCAs atwhich its tree structure terminates. These are referred to herein asleaf PCAs 2108. The other PCAs, between the root PCA 2104 and the leafPCAs 2108 in the tree, are referred to as intermediate PCAs 2106.

FIGS. 22-26 illustrate clustering operations. FIG. 22 illustrates a joinoperation. In a join operation, a PCA which does not currently belong toany cluster joins to another PCA or a member of an existing PCA cluster.As shown in FIG. 21, PCA2 is being joined to PCA1 to form a cluster2202. Subsequently, PCA3 is joined to the cluster 2202 of PCA1 and PCA2.

FIG. 23 illustrates a second clustering operation, called “leave.” Inthis operation, a leaf PCA or an intermediate PCA leaves a PCA cluster.In FIG. 23, PCA3 severs itself from a cluster 2302 consisting of PCA1and PCA2. The resulting cluster 2302 includes only PCA1 and PCA2.

FIG. 24 illustrates a third operation, called “cluster merge.” In acluster merge, a root PCA joins to a PCA or a member of a preexistingPCA cluster. In FIG. 24, a cluster 2402 consisting of PCA1, PCA2 andPCA3 are merging with a cluster 2404 consisting of PCA4 and PCA5. Themerged cluster 2406 includes all of PCA1, PCA2 and PCA3, PCA4 and PCA5.PCA1 was the root cluster for cluster 2402 and is the root cluster forthe merged cluster 2406.

FIG. 25 illustrates a fourth operation, called “cluster prune.” In thisoperation, a root PCA or intermediate PCA prunes or removes successivesets of PCAs from the original cluster. PCAs of the resulting clustersbecome the root PCAs for the respective clusters. As shown in FIG. 25,an initial cluster 2502 results in two separate clusters 2504, 2506.Cluster 2504 consisting of PCA4 and PCA5 severs itself from a cluster2506 consisting of PCA1, PCA2 and PCA3.

FIG. 26 illustrates a last operation, called “cluster devolution.” Inthis operation, a root PCA leaves a cluster and transfers clusterinformation to a successor root cluster. In FIG. 26, PCA1 is the rootPCA of the cluster 2602. PCA1 leaves the cluster 2602, leaving the otherPCAs behind. PCA2 becomes the root PCA of the remaining cluster 2602.

The table below shows the messages used in one embodiment of the systemand method described herein. {JOIN REQ, ALLOW JOIN, DENY JOIN} is amessage set of the Join operation. {LEAVE REQ, LEAVE ACK} is a messageset for the Leave operation. {PRUNE REQ, PRUNE ACK} is a message set forthe Prune operation. There are no ALLOW or DENY messages for the Leaveand Prune operations. The last message is used for traffic reporting.These messages are conveyed hop-by-hop through the master-slaverelations in the paging clusters.

TABLE Protocol Messages Message Description Sender Receiver JOIN REQSent to join a cluster ROOT ROOT A LLOW JOIN Permit JOIN REQ ROOT ROOTDENY JOIN Reject JOIN REQ ROOT ROOT LEAVE REQ Sent to leave a clusterBRANCH, LEAF ROOT LEAVE ACK Ack of LEAVE REQ ROOT BRANCH, LEAF PRUNE REQSent to prune a tree ROOT BRANCH, LEAF PRUNE ACK Ack of PRUNE REQBRANCH, LEAF ROOT PMAP PMAP report BRANCH, LEAF ROOT REPORT

Initially, the base station routers (BSRs) are isolated. All the BSRsexecute procedure Main( ) in the beginning of each bootstrap round. Oneembodiment of procedure Main( ) is shown below. During the execution ofthe procedure, the BSRs are partitioned into clusters. A cluster is aset of interconnected BSRs. A cluster can include a single BSR. There isonly one ROOT BSR in each cluster. For a single BSR cluster, the onlymember is the ROOT BSR. When a ROOT BSR retires, it stops being a ROOTand will be inactive for the rest of the ROOT algorithm, unless itbecomes a ROOT again.

The procedure Main( ) calls a procedure depending on the BSR's status.If the BSR is a ROOT, it calls Root Main( ). Otherwise, it calls aprocedure Other Main( ). Since this is an asynchronous distributedalgorithm, a Lock mutex variable is defined to protect critical sectionswithin a BSR.

Main ( ) { // Main for all 1 prepare a mutex Lock; 2 variable v is thisBSR; 3 while true { 4 if (v == ROOT) 5 Root Main (v) ; 6 else 7 OtherMain (v) ; 8 } 9 }

The procedure Root_Main( ) waits for messages defined in the table aboveduring T period. The procedure Wait_For_Input( ) is used for acceptingasynchronous inconing requests. When the procedure Wait_For_Input( )returns, it executes a procedure Root_Msg_Recv( ), which handlesreceived messages. A constant T is assumed, such that user movement andpaging traffic statistics are sampled in T period. A choice of T can beset by operators.

After the time period T, the procedure Root_Main( ) calls procedureRoot_Trigger( ). This procedure decides whether the ROOT BSR takes ajoin or prune action. The procedure Root_Trigger( ) is described ingreater detail below.

Root_Main (v) { // Main for ROOT  1 var_BSR u;  2 t₀ = current_time ( );  3 while (current_time ( ) - t₀ T period) {  4 Wait_For_Input(&Root_Msg_Recv ( ) , timeout) ;  5 }  6 switch (Root_Trigger (v, PMAP,&u)) {  7 case JOIN :  8 Join (u, v) ; break ;  9 case PRUNE : 10 Prune( ) ; break ; 11 case default : 12 break; 13 } 14 return; 15 )

The procedure Root_Msg_Recv( ) is called in the procedure Root_Main( ).It processes received messages. A PMAP REPORT message is received from aslave BSR. All of the PMAP information within a cluster must be reportedto the ROOT BSR so that it can detect all the neighboring paging areas.A JOIN REQ message comes from another ROOT BSR, which requests to jointo the cluster. The message JOIN REQ must contain the requesting ROOTBSR's current PA-ID to prevent a master-slave looping. A LEAVE REQmessage comes from a slave BSR, which requests to leave the cluster. Theprocedure Root_Msg_Recv( ) also needs to acquire the lock after itreceives a message to avoid data inconsistency. If it fails to acquirethe lock, it just sends an error message to the previous sender.

Root_Msg_Recv (v) { // Message handler for ROOT  1 msg = receiver ( ) ; 2 if (acquire (Lock) == true) {  3  switch (msg.type) {  4 casePMAP_REPORT:  5 PMAP  msg.body; break;  6 case JOIN REQ:  7 Join_hdr(msg, v) ; break;  8 case LEAVE_REQ:  9 Leave_hdr (msg, v) ; break; 10 } 11  release (Lock) ; 12 }  else { 13 send (msg.sender, ERROR) ; 14  }15 }

The procedure Join_hdr( ) handles a join request from another ROOT BSR.Since this is a distributed procedure, it might have old informationabout the neighboring paging areas. The procedure fetches neighborinformation by requiring PMAPs of the current slaves. Then, the ROOTcalculates CostChange( ), a procedure which is described below indetail. If the result of the procedure CostChange( ) is positive, theJoin_hdr( ) procedure checks the maximum size K of the cluster. If thesize of the cluster is below K, the ROOT BSR allows to join. Then, itmust update the tree topology and neighbor information related to thejoin operation. Finally the ROOT BSR sends out the ALLOW JOIN message tothe sender. Otherwise, it replies by DENY JOIN. This procedure also mustbe carried out within the mutex lock.

Join_hdr (msg, v) { // Join request handler  1 fetch current PMAP infofrom slaves;  2 if (CostChange (v) == positive) {  3 if (total size ofthe cluster K) {  4 msg.sender added to the cluster ;  5 Update topologyinformation;  6 Update neighbor information;  7 send (msg.sender,ALLOW_JOIN) ; return;  8 } else  9 send (msg.sender, DENY_JOIN) ;return; 10  else 11 send (msg.sender, DENY_JOIN) ; return; 12 }

The Leave( ) procedure deals with a leave request. A ROOT BSR allows aBRANCH and LEAF BSRs to leave at anytime. The Leave( ) procedure updatesthe tree topology by cutting off the requester. After that, the ROOT BSRjust sends an acknowledgement.

Leave-hdr (msg, v) { // Leave request handler 1 msg.sender removed fromthe cluster; 2 send (msg.sender, LEAVE_ACK) ; 3 }

The Join( ) procedure is called after the ROOT BSR decides to join toanother cluster. It must acquire the lock before sending the message. Ifthe other ROOT BSR allows the ROOT BSR to join, the requester receivesan ALLOW_JOIN message. Then, the requester ROOT BSR retires from a ROOTand starts being a BRANCH or LEAF.

Join (u, v) { // Join request sender  1 if (acquire (Lock) == true) {  2send (u, JOIN_REQ) ;  3 msg = receive ( ) ;  4 if (msg.type ==ALLOW_JOIN) {  5 v retires from root;  6 release (Lock) ;  7 return;  8} else if (msg.type == DENY_JOIN) {  9 release (Lock) ; 10 return; 11  }12 } else 13 return; 14 }

The procedure Prune( ) is called after the ROOT BSR decides to prunesome of the BRANCH trees or LEAFs within the cluster. This prunedecision is made in Root Trigger( ), which is described below.

Prune (v) { // Prune request sender  1  if (acquire (Lock) == true) {  2for each remaining w 2 v's slaves;  3 send (w, PRUNE_REQ) ;  4 msg =receive (w) ;  5 if (msg.type == PRUNE_ACK)  6 Separate w;  7 else  8return;  9 } 10  }

The procedure Other_Main( ) is for the BRANCH and LEAF BSRs. After thetime period T, it sends a PMAP report to its ROOT BSR. The BRANCH andLEAF BSRs are allowed only one voluntary operation, Leave. The procedureOthers_Trigger( ) decides to leave or stay in the current cluster, whichis described below. Once a BSR decides to leave, it sends a LEAVE_REQmessage to the ROOT BSR. If the requesting BSR receives a permissionfrom the ROOT BSR, it updates the topology and neighbor information.Note that the leave operation is not allowed when the BSR is in the ROOTstatus.

Other_Main (v) { // BRANCH and LEAF's Main  1 t₀ = current time ( ) ;  2while (current time ( ) - t0  T period) {  3  Wait For Input(&Other_Msg_Recv, timeout) ;  4 }  5 send (master, PMAP_info) ;  6 if(Leave_Trigger (PMAP, v) == negative) {  7 acquire (Lock) ;  8 send(ROOT, LEAVE_REQ)  9 msg = receive (ROOT) ; 10  if (msg.type ==ALLOW_LEAVE) { 11 Update topology information; 12 Update neighborinformation; 13 release (Lock) ; 14 return; 15  } ; 16  release (Lock) ;17  return; 18  } 19 }

The BRANCH and LEAF BSRs are supposed to accept four messages during theperiod T. When a BRANCH or LEAVE BSR receives a JOIN_REQ and LEAVE_REQmessage, it simply forwards to the master BSR. If a BSR receives themessage FETCH_REQ, it sends back its PMAP information to the requester.When a BSR receives PRUNE REQ it executes Prune( ) operation to leavefrom the current cluster with slave BSRs beneath. Note that in thevoluntary leave, the BSR leaves without the slaves. However in theprune, the BSR leaves with the slave BSRs.

Other_Msg_Recv (v) { // Message handler for Others  1 msg = receive ( );  2 if (acquire (Lock) == true) {  3 switch (msg.type) {  4 caseJOIN_REQ  5 send (master,msg) ; break;  6 case LEAVE_REQ  7 send(master,msg) ; break;  8 case PRUNE_REQ  9 Prune (v) ; break 10 caseFETCH_REQ 11 send (msg.sender, PMAP) ; break; 12  } 13 else 14 send(msg.sender, ERROR) ; 15 } 16 release (Lock) ; 17 }

Trigger functions utilize statistical tables made by the trafficsamplings described above. A ROOT BSR can decide whether to join anothercluster or to prune the tree.

Root_Trigger (v, PMAP, *u) {  1  var int max, min, tmp;  2  var_BS w;  3neighbor_list find_PAneighbors (PMAP) ;  4 if (Cost (v) >PruneThreshold) {  5 return prune;  6 }  7 for each remaining w εneighbor_list {  8 tmp = CostChange (w) ;  9 if (min > tmp) { 10 min =tmp; 11 u w; 12 } 13  if (min < JoinThreshold) { 14  u removed fromneighbor list; 15  return join; 16 } 17 } 18 }

In the beginning, Root_Trigger( ) tries to find neighboring paging areasby using collected PMAP. Then, it begins to calculate a prune trigger.If the paging cost exceed a certain limitation, the paging area sizeshould be reduced so that it won't occupy too much wireless bandwidth.If the result of Cost( ), which is described below is larger than thevalue of the variable Prune Threshold, all the branches are untied to beindependent BSRs.

Next, Root_Trigger calculates the join trigger. A ROOT BSR is able toknow all the slave's PMAP, which is reported from the slave to its root.The collected PMAP provides the ROOT BSR the marginal probabilitydistribution of neighboring paging areas. The join trigger searches allthe possible neighbors by looking up PMAP. For each candidate, itcalculates function Cost_Change( ), which is described below.Root_Trigger( ) searches minimum cost join candidate. If the candidateis below the value of the variable JoinThreshold, the ROOT base stationdecides to join to it.

If the value of the variable JoinThreshold is set large enough, a ROOTBSR learns to joins to others faster.

The procedure Leave_Trigger( ) is the only operation that non-ROOT BSRsexecute. Every BSR maintains its PMAP and if the BSR estimates themovement within the current cluster is lower than another paging area,it tries to leave the current cluster.

Leave_Trigger (PMAP, v) { 1  refresh PMAP information; 2  for eachremaining w ε PMAP { 3 if (current cluster is lower than w) 4 returnnegative; 5  } 6  return positive; 7 }

Initially, the procedure Leave_Trigger( ) refreshes PMAP information.Then, the BSR compares the marginal probability distributions in PMAPwith that of current cluster. If the value for the current cluster islower than the others, it decides to leave by returning a negativevalue. Otherwise, it remains in the same cluster.

Note that when two cells are in same paging area, then a dormant modeuser will not update its location information when it moves betweenthose two cells. This is because a mobile host will not enter the activemode until it hears a different PA-ID. As a result, no location updatemessage with which the user traffic is monitored will be sent. This maybe referred to as a hidden movement problem. When the inner trafficpattern has changed, the old pattern may become costly, as cost is usedherein. Under these circumstances, the BSR must be able to detach itselffrom the old paging area so that it can choose the best new paging areato join. In order to solve this problem, a simulated annealing method isproposed. In every entry refresh in PMAP, a BSR calculates the followingequation:τ_(pv)(t+1)=(1−ρ)τ_(pv))t)where τ_(pv) (t) is the current traffic information and ρε[0,1] is aconfigurable constant which decides how fast the cell becomesindependent.

The meaning of this equation is straightforward. If a boundarydisappeared since the cell joined a paging area, the algorithm assumesthe traffic on that boundary begins to decline. When the τ_(pv)(t+1) islower than a certain threshold, the algorithm will make the cellindependent to perform the join action again. As a result, after acertain period, the cell will become independent. When a cell findsthere is no different paging area on its boundaries, the annealingalgorithm will not be performed.

The algorithm described herein depends on the proper trigger tojoin/leave paging areas. Since one of the targets of dynamic paging areaconstruction is to minimize the overall paging cost, it is natural touse a cost function as the trigger. As discussed above, the overallpaging cost can be divided into two parts, the paging cost and locationupdate cost.

Paging Cost

The paging cost is defined as the bytes/sec which are transmitted withina paging area when an incoming call is received. The paging cost can befurther divided into two types: the cost for wired and the cost forwireless channels. In order to measure the paging cost, the followingparameters are defined:

-   -   PAi—the ith Paging Area    -   Ri—the incoming call rate of paging area i (PAi) (call/sec)    -   Cp—the paging cost in a cell for a call (bytes/(call-celi))    -   Ncells(i)—The number of cells in the paging area i (cell)

Furthermore, αC_(p) is the cost of sending a paging request from arouter to another, and βC_(p) is the cost of broadcasting a pagingrequest on the air. α and β are weights for wire and wirelesstransmission. For each incoming call for PAi, we assume that the pagingmessage is transmitted only once to each cell and then broadcasted onthe air. The paging cost is then described in the following equation:Cost_(incoming)(i)=R ₁×(α+β)×N _(cells) ×C _(p)

Location Tracking Cost

When a user moves from his old PAj into a new PAi, it has to update thelocation information. The Location Update Cost is defined as number ofbits that are transmitted per-second when a user crosses the boundariesseparating two different paging areas. Note that if two cells are in thesame paging area when a user crossed the boundaries of these two cells,the user will not update the information. In order to measure thislocation update cost, the following parameters are defined:

-   -   pji—the rate of users moves from PAj to PAi.(usersec)    -   pij—the percentage of users moves from PAi to PAj. (usersec)    -   dBSRi;TAi—The average distance, i.e. number of hops, between the        BSR and TA in PAi (hops)    -   dBSRi;DMAi—The average distance, i.e. number of hops, between        the BSR and DMA in PAi (hops)    -   Cu the location update cost per hop (bytesuser¢hop)    -   N(i) the set containing the paging area adjacent to PAi, does        not include PAi.

For each paging area i

${{Cost}_{{location} - {update}}(i)} = {\sum\limits_{j \in {N{(i)}}}{2{p_{ji}\left\lbrack {{\alpha\left( {d_{{BSR}_{i},{TA}_{i}} + d_{{BSR}_{i},{DMA}_{i}}} \right)} + \beta} \right\rbrack}C_{u}}}$

Total Paging Cost

Based on the cost functions presented herein, the total cost during acertain time period is defined as follows:

${Cost} = {{R_{i} \times \left( {\alpha + \beta} \right) \times N_{cells} \times C_{p}} + {\sum\limits_{j \in N_{i}}{2{p_{ji}\left\lbrack {{\alpha\left( {d_{{BSR}_{i},{TA}_{i}} + d_{{BSR}_{i},{DMA}_{i}}} \right)} + \beta} \right\rbrack}C_{u}}}}$

Based on this equation, 3 parameters, incoming call rate, size of thepaging area, and traffic information between two paging areas contributeto the total cost significantly. Next, the relationship between theseparameters and dynamic paging area construction is analyzed.

Traffic Pattern

Based on the cost function, it can be seen that the traffic between twopaging areas contributes to the paging cost significantly. Intuitively,when the traffic between two different paging areas is heavy enough, bycombining two cells, it is possible to reduce the overall paging costsince less location update information is transmitted. Based on thisfact, triggering of the join action will be analyzed.

Consider two paging areas, i,j, which are adjacent to each other. Thenbased on the cost function above, during a fixed period, the cost ofpaging area i is

${Cost}_{i} = {{R_{i} \times \left( {\alpha + \beta} \right) \times {N_{cells}(i)} \times C_{p}} + {\sum\limits_{k \in {N{(i)}}}{2{p_{ki}\left\lbrack {{\alpha\left( {d_{{BSR}_{i},{TA}_{i}} + d_{{BSR}_{i},{DMA}_{i}}} \right)} + \beta} \right\rbrack}C_{u}}}}$

The total cost during period T iscost=costi+costj

After we combine the two PAi and PAj, during the same period of T, thetotal cost is

${Total} = {{\left( {R_{i} + R_{j}} \right) \times \left( {\alpha + \beta} \right) \times \left( {\left( {{N_{cells}(i)} + {N_{cells}(j)}} \right) \times C_{p +}} \right)} + {\sum\limits_{{k \in {{N{(i)}}\bigcup{N{(j)}}}},{k \neq j},i}{2{p_{ki}\left\lbrack {{\alpha\left( {d_{{BSR}_{i},{TA}_{i}} + d_{{BSR}_{i},{DMA}_{i}}} \right)} + \beta} \right\rbrack}C_{u}}}}$

Subtract from the total paging cost before combining them together

Cost_(change) = ((R_(i)N_(j) + R_(j)N_(i)) × (α + β) × C_(p) − 2p_(ji)[α(d_(BSR_(i), TA_(i)) + d_(BSR_(i), DMA_(i))) + β]C_(u) − 2p_(ji)[α(d_(BSR_(i), TA_(i)) + d_(BSR_(i), DMA_(i))) + β]C_(u)

If the distance is similar, we then have the following equation

Cost_(change) = ((R_(i)N_(j) + R_(j)N_(i)) × (α + β) × C_(p) − 2p_(ji)[α(d_(BSR, TA) + d_(BSR, DMA)) + β]C_(u)

where pi;j=pij+pji and it represents the all the traffic between the twodifferent paging areas. It is clear that when the Cost_(change) is lessthan 0, by combining two paging areas, the overall paging cost can bereduced. The combination process only impacts the overall paging cost ofthe two paging areas involved.

Incoming Call Rate

Triggering of the join action was discussed above. In some situations,the upper bound for the paging cost is fixed. For example, the operatorcan set the upper bound of the cost function so that it won't occupy toomuch wireless bandwidth. This situation can be referred to as a FixedEnergy Budget environment. When the paging area is stabilized and theincoming rate increases significantly, by reducing the size of thepaging area, the cost can be reduced to the original level. In thepresently disclosed embodiments, the prune action is always triggeredunder this circumstance.

FIGS. 27-35 illustrate communication during clustering operationprocedures. In the illustrated embodiment, there are six procedures: amovement report procedure, the join procedure, the leave procedure, thecluster merge procedure, the cluster prune procedure and the clusterdevolution procedure. Each of these will be described in turn.

FIG. 27 illustrates communication during a movement report procedure. Asshow in FIG. 27, a mobile host (MH) is currently registered in acommunication network with a last hop router of the network, designatednLHR. The MH travels and conducts 2702 a layer 3 hand-off from nLHR to alast hop router designated n+1LHR. Any conventional hand-off proceduresuitable for the communication network may be used. The MH then reports2704 its movement into the n+1LHR or registers with the n+1LHR.

FIGS. 28 and 29 illustrate the second procedure, the “joiningprocedure.” In FIG. 28, PCA1 is joining to PCA2. PCA1 first sends 2802 arequest to join to PCA2. If PCA1 is allowed to be joined, PCA2 sends2804 a reply to PCA1 accepting the joining PCA1. After being joined withPCA1, PCA2 becomes a root PCA. PCA2 switches from the defaultinformation (FIG. 14) to the root information (FIG. 16) and updates theroot information to add PCA1 to the root information as a subordinatePCA. PCA1 becomes dependent from PCA2. PCA1 switches from the defaultinformation to the branch information (FIG. 15) to add PCA2 to it as itsroot PCA.

One PCA may join a cluster of PCAs. As shown in FIG. 29, PCA1 is aboutto join a cluster consisting of PCA4, PCA 3 and PCA2. In this cluster,PCA4 is the root PCA, PCA3 is an intermediate PCA, and PCA2 is a leafPCA. PCA1 first sends 2902 a join request to PCA2. Retrieving itscluster map (CMAP), PCA2 forwards 2904 the request to its immediatepredecessor PCA3, which likewise forwards 2906 the join request to theroot PCA, PCA4. If joining of PCA1 is acceptable, PCA4 sends 2910 areply accepting joining with PCA1. This reply is forwarded 2912 thoughPCA3 and forwarded 2914 through PCA2 to PCA1. PCA4, PCA3 and PCA2 addPCA1 to their CMAPs as a distal PCA connected to PCA2 in their treestructure.

The third procedure is called a “leave procedure.” FIGS. 30-32illustrate examples of the leave procedure. In FIG. 30, PCA4, PCA3, PCA2and PCA1 form a cluster in which PCA4 is a root PCA, PCA1 is a leaf PCA,and PCA3 and PCA2 are intermediate PCAs. PCA1 is about to sever itselffrom the cluster. A request from PCA1 is forwarded 3002 to PCA4 thoughintermediate PCAs 2 and 3. PCA4 in return sends 3004 a reply to PCA1through the same path in the reverse direction. After PCA1 is severedfrom the cluster, PCA4, PCA3 and PCA2 delete PCA1 from the cluster treein their CMAPs.

FIG. 31 shows another example of the leave procedure in which PCA2 issevering itself from the cluster. PCA2 sends 3102 a request to PCA4through PCA3. PCA4 in response returns 3104 a reply to PCA2 throughPCA3. In the meantime, PCA2 also sends 3106 the same request to PCA1,which returns 3108 a reply back to PCA2. After PCA2 is severed from thecluster, PCAs 4 and 3 delete PCA2 from the cluster tree in their CMAPs.PCA1 switches to the default information and then sends 3110 a requestto join to PCA3. The procedures for joining PCA1 to the clusterconsisting of PCA3 and PCA4 are the same as described above.

FIG. 32 shows another example of the leave procedure in which PCA3 issevering itself from the cluster. PCA3 sends 3202 a request to disjointo PCA4. PCA4 returns 3204 a reply to PCA3. In the meantime, PCA3 sends3206 the same request to PCA2, which returns 3208 a reply to PCA3. AfterPCA3 is severed from the cluster, PCA4 switches back to the defaultinformation. PCA2 then sends 3210 a request to merge to PCA4. Theprocedures for merge are already described above.

FIG. 33 illustrates the fourth procedure, called a “cluster mergeprocedure.” As shown in FIG. 33, a cluster including PCA1 is merging toa cluster consisting of PCA4, PCA3 and PCA2. PCA4 is the root PCA in themerged cluster. The merging cluster may include other PCAs than PCA1,which is the root PCA in the merging cluster. PCA1 sends 3302 a requestto merge to PCA2, which forwards 3304 the request to PCA4 through PCA3.If the merge is not going to violate any overlapping constraint or otherconstraints, PCA4 returns 3306 a reply to PCA1 which is forwarded 3308through intermediate PCAs 3 and 2. After the merge is completed, PCA4,PCA3 and PCA2 update their CMAPs to add the merging cluster includingPCA1 that becomes subordinate to PCA2. Likewise, the PCAs in the mergingcluster also update their CMAPs.

The fifth procedure is called a “cluster prune procedure.” In FIG. 34,there exists a cluster consisting of PCA3, PCA2 and PCA1, where PCA3 isthe root PCA, and PCA2 and PCA1 are intermediate PCAs. PCA2 wishes tosever PCA1 and itself from PCA3. PCA2 also wishes PCA1 to become theroot PCA of the resulting cluster. PCA2 sends 3402 a request to prune toPCA3 and sends 3404 a request to PCA1. If the prune is acceptable, PCA3and PCA1 send 3406, 3408 replies to PCA2. PCA1 and PCA2 are firstsevered from PCA3. PCA3 switches back to the default information. PCA1then becomes a root PCA, and PCA2 becomes subordinate to PCA1. PCA1switches to the root information including PCA2 as a subordinate.

The last procedure is called a “cluster devolution procedure.” In FIG.35, there is a cluster consisting of PCA3, PCA2, PCA1 and PCA0. In thiscluster, PCA3 is the root PCA of the cluster. PCA2 and PCA3 aresubordinate to PCA3 at the same level. PCA0 is dependent from PCA1. PCA3is severing itself from the cluster and sends 3502 a request to serveritself to PCA2. The request includes the information in the CMAP of PCA3that indicates the tree structure of the cluster. PCA2 returns 3504 areply to PCA3. Then, PCA1 severs itself from the cluster. At the sametime, PCA2 becomes the root PCA. If PCA3 wishes PCA1 to become a rootPCA, it may send the same request to PCA1, instead of PCA2. PCA2, as theroot PCA, notifies 3506 PCA1 and PCA0 of the cluster structure. Inreturn, PCA1 and PCA0 send 3508 an acknowledgement to PCA2.

While a particular embodiment of the present invention has been shownand described, modifications may be made. It is therefore intended inthe appended claims to cover such changes and modifications which followin the true spirit and scope of the invention.

1. A last hop router configured for use in a telecommunication system,the last hop router comprising: a paging area clustering agent toreceive movement reports from mobile hosts in the telecommunicationsystem, to determine dynamic clustering of paging areas based uponstatistical mobility information derived from the movement reports, andto send paging messages to local paging agent clusters to page a mobilehost; a dormant monitoring agent to detect delivery of packets addressedto a mobile host in dormant mode and activate the paging area clusteringagent to send a paging message to the local paging agent clusters topage the mobile host; and a local paging agent for sending pagingsignals to mobile hosts identifying a paging area associated with thelast hop router, wherein the paging area clustering agent performs thefollowing processes: a probability map update process, wherein theprobability map update process receives a registration signal from amobile host, calculates statistics of mobile host movement and updatesthe probability map, and determines frequencies of mobile host movementsand notifies the clustering process; a clustering process, wherein theclustering process locates and determines paging areas to be joined ordisjoined from other paging areas and updates the cluster maps of thepaging area and other paging areas; and a paging forwarding process,wherein the paging forward process receives a paging trigger packet fromthe dormant monitoring agent and queries the cluster map to determine towhich area a packet should be delivered, forwards the paging triggerpacket to the area, and notifies the clustering process of frequenciesof paging trigger packets received.
 2. A paging forwarding processoperative in conjunction with a telecommunication system including aplurality of access points capable of radio communication with aplurality of mobile hosts, the paging forwarding process comprising:clustering map discovery means for determining in a clustering map towhich paging areas of the telecommunication system packets should bedelivered to in response to a received paging trigger packet; pagingforwarding means for forwarding the paging trigger to a paging areadetermining by the clustering map discovery means; and pagingnotification means for tracking frequencies of receipt of paging triggerpackets.
 3. A join method for clustering of paging areas in atelecommunication system, the join method comprising: at one accesspoint of the telecommunication system, detecting another access point tojoin; sending a request to join the other access point; after joining,at the one access point, substituting branch clustering information fordefault clustering information; and specifying the other access point asa root wherein detecting another access point to join comprises: storinga probability map of information about movement of mobile hosts in thetelecommunication system; and based on the probability map, identifyingpaging areas to be joined.
 4. A join method for clustering of pagingareas in a telecommunication system, the join method comprising: at aleaf access point of a paging area cluster of access points of thetelecommunication system, receiving from a joining access point arequest to join the paging area cluster, wherein the paging area clusterincludes a paging area for each of the access points of the paging areacluster; within the paging area cluster, forwarding the request throughone or more predecessor access points to a root access point; at theroot access point, determining if joining is permitted; if joining ispermitted, sending a reply from the root access point through the one ormore predecessor access points to the leaf access point forcommunication to the joining access point.
 5. A cluster merge method forclustering of paging areas in a telecommunication system, the clustermerge method comprising: at a first paging area cluster of accesspoints, receiving a request to merge from a second paging area clusterof access points; forwarding the request to a root of the first pagingarea cluster; determining at the root if the request to merge may begranted; returning a reply to the second paging area cluster; and aftermerging the first paging area cluster and the second paging areacluster, at access points of the first paging area cluster of accesspoints, updating stored clustering data to reflect the merging.
 6. Acluster prune method for clustering of paging areas in atelecommunication system, the cluster prune method comprising: at oneaccess point of a paging area cluster of access points, originating arequest to prune to other access points of the paging area cluster ofaccess points; receiving a reply from the other access points; andsevering one set of access points of the paging area cluster of accesspoints from another set of access points.
 7. The cluster prune method ofclaim 6 wherein originating a request to prune comprises: identifyingone or more access points to sever from the paging area cluster to forma new cluster; and identifying an access point of the one or more accesspoints to become a root of the new cluster.
 8. A cluster devolutionmethod for clustering of paging areas in a telecommunication system, thecluster devolution method comprising: at a root access point of a pagingarea cluster of access points, originating a request to devolve to otheraccess points of the paging area cluster of access points, the requestincluding information defining a tree structure of the paging areacluster; receiving a reply at the root access point; and in response tothe reply, severing from the paging area cluster.
 9. The clusterdevolution method of claim 8 further comprising: receiving the requestat a second access point; sending the reply to the root access point;and after the severing, notifying other access points of the paging areacluster that the second access point is a new root access point.